Rotary fan.



No. 7l3,990. Patented Nov. l8, I902.

. J. KEITH.

ROTARYFA N.

App1icafiion filed May 20, 1902.)

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No. 7|3,990. Patented Nov. I8, 1902. J. KEITH. ROTARY FAN.

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UNITED TA'r'Es EDATENT Prion.

JAMES KEITH, OF LONDON, ENGLAND.

ROTARY FAN.

SPECIFICATION forming part of Letters Patent No. 713,990, dated November18, 1902.

Application filed May 20, 1902. Serial No. 108,256. (No model.)

To CLZZ whom, it may concern;

Be it known that I, JAMES KEITH, a subject of the King of the UnitedKingdom of Great Britain and Ireland, residing at 27 Farrington avenue,London, England, have invented certain newand useful Improvements inRotary Fans, (for which application for patent has been made in GreatBritain, No. 6,267, dated March 13, 1902,) of which the following is aspecification.

The subject of this invention is a duplex fan composed of a set ofblades of the Blackman or scooped type formed around an open drum orshell center and a set of blades of the screw type so arranged aroundand behind the Blackman type of blades or around a cone on a singlerotating shaft that the one set of blades serve to draw in air anddeliver it to the second set of blades, by means of which the propulsiveor compressive action is reinforced, and a larger volume of air or agreater pressure is obtained for a given size and speed, than isattainable with the ordinary single fan.

In the accompanying drawings, Figure 1 is a side elevation of thecomplete duplex fan. Fig. 2 is an elevation showing the inlet side ofthe fan with the blades of the Blackman or scooped type. Figs. 3 and 4are corresponding views showing a modification of the duplex fan.

In the embodiment of the invention shown by Figs. 1 and 2 the duplex fanis composed of a set of blades a of the Blackman or scooped typeextending from an open drum or shell center f, fixed by arms to a hubwhich is mounted upon a central rotatable shaft d, the outer edges ofthe blades being attached to a rim 6 in the usual way. The fan comprisesalso a second set of blades 12, which are of the screw type or areapproximately parallel with the shaft (1 and are attached to the shaft dor to the open drum or shell center f, in which a cone is or may befixed. When the cone 0 is used, it increases in diameter toward thedischarge side of the fan, and it tends to direct the air which passesthrough the blades a and the open drum or shell center f toward the mosteffective position at the outer ends of the blades 1), while alsopreventing return fiow of the airthrough the center of the fan. The

blades 1) are preferably more numerous than the blades or, so that theycross or partly cross the delivery edges thereof, and the blades a and band the open drum or shell center f thus fill as far as possible thearea of the circle in which they rotate, while leaving at the same timesufficient space for the free and untrammeled entrance and exit of theair. By this arrangement the effective area of the blades a, which istoward the periphery of the fan, is retained, the area near the centerof rotation being of little effective value, and an inlet is providedthrough which additional air is induced by the blades 1) and directed bythe cone 0 when used toward the said screw-blades b, by which it isdelivered. The conical boss 0 when used is carried through the centralparts of the fan for directing the infiowing air toward the blades b andfor preventing return flow of the air discharged by the fan.

-In Fig. 2 the dotted lines show the screwblades b, whose feed edges(indicated by thicker lines) cross the discharge side of the scoopedblades a.

In the modification shown by Figs. 3 and 4 the duplex fan is of the sameconstruction as that described; but the scoopedfan-blades a instead ofending at and being attached to v the open drum or shell center f arecontinued toward the front part of the central conical boss 0 on theshaft.

A duplex fan constructed as described differs essentially from twoindependent fans running on the same axis, inasmuch as in the lattercase the second fan may only act to retard the flow of the air from thefirst fan and if the fans be open will have no reinforcing efiect, whilein the duplex fan the one set of blades delivers the air induced bytheir rotation directly to the second set of blades, by means of whichits forward propulsion is reinforced and a greater pressure or greatervolume of air results, according as the central boss is made larger orsmaller.

Having now described the invention, what I desire to claim and secure byLetters Patent is' 1. A duplex fan composed of two sets of fan-blades onthe same rotating shaft of which one set is of the scooped or Blackmantype and is arranged to deliver air induced by its rotation to thesecond set of blades which are of the screw type, the Blackman type ofblades being formed around an open drum or shell center wherein anannular opening is formed on the inlet side of the fan to lead in theair to the second set of air-blades which *are closed centrally againstreturn flow of the air by a central conical boss.

2. A duplex fan composed of two sets of fan-blades on the same rotatingshaft of which one set is of the scooped or Blackrnan type, and isarranged to deliver air induced by its rotation to the second set ofblades which are of the screw type, the blades being secured around acentral conical boss which serves to induce the air to the fan-bladesand prevents return flow of air through the center of the fan.

In testimony whereof I have hereunto set my hand in presence of twowitnesses.

JAMES KEITH.

W'itnesses:

WALLACE FAIRWEATHER, J NO. ARMSTRONG, Jr.

